Hair follicle microbiome: differences associated with skin diseases, with no established causality

A synthesis of 55 studies with widely varying methods

Hair follicles are skin microenvironments that host their own microbial communities. The authors searched six bibliographic databases for studies published between 2007 and August 2024 on their bacterial microbiome in various inflammatory diseases.

The review brings together 55 studies conducted in 19 countries. All used methods independent of bacterial culture. However, there were substantial differences in sampling, storage, DNA extraction, sequencing and analysis. The researchers therefore conducted a qualitative synthesis, without providing a pooled numerical estimate of the observed differences in the abstract.

Recurring findings, but no universal signature

Staphylococcus showed increased relative abundance in several diseases, including scarring alopecias, seborrheic dermatitis or dandruff, and acne. Relative abundance describes the proportion of a bacterial group within the community analyzed, not necessarily an increase in its total amount.

For Cutibacterium, the findings depended more on the disease. Its abundance was reduced in seborrheic dermatitis and dandruff, while the species Cutibacterium acnes appeared more prevalent in androgenetic alopecia. Findings were inconsistent in scarring alopecias and acne.

Data on alopecia areata and rosacea remained inconclusive. In hidradenitis suppurativa, they suggested an enrichment of opportunistic anaerobic bacteria, including Porphyromonas and Prevotella.

An association does not yet identify a therapeutic target

The main finding is the recurrence of certain bacterial differences across diseases. It does not demonstrate that correcting these differences would improve symptoms. The authors consider their causal significance uncertain and call for larger, standardized studies accompanied by functional analyses.

When making a purchase decision, this review therefore does not validate a supplement targeting the skin microbiome. It describes associations, not the effectiveness of an intervention. The source dossier provides access only to the PubMed abstract: the full text, funding and conflicts of interest have not been checked.

What we can take away

The follicular microbiome is associated with several skin diseases, but this review neither establishes a bacterial cause nor supports recommending a treatment aimed at modifying it.